Scientific advances and innovation

Since 20 years, one single definition of roughness due to marine-growth is recommended for hard marine growth. Recent measurements carried out by University of Nantes show high heterogeneity of the size and the density of individuals. Preliminary studies with Total and Ifremer showed an increase of 20% of the loading due to micro-roughness. The innovation relies on the building of a new definition of the roughness that facilitates the relationship with on site measurement with the Aksi-3D device, developed by University of Nantes and MAREI (Ireland).

Expected technical and economic impact

  • Improve the modelling of hydrodynamic coefficients for engineers in presence of marine growth
  • In view to optimize MRE design and reduce system maintenance costs
  • By improving the definition of roughness due to hard marine macro-organisms

Key project milestones

  • April 2017 - Project kickoff
  • October 2017 - Bibliography synthesis Unifed definition of roughness
  • April 2018 - Tests requirements and computation test based
  • April 2020 - New definition and model

Demonstrator

Two test sites were used to characterize biocolonization: the two sites at sea SEMREV (Central School of Nantes) and UN@SEA with the measurement station Biocolmar (University of Nantes). The measurements were carried out with the Aksi3D protocol of the University of Nantes. IFREMER’s hydrodynamic basins have been used to characterize hydrodynamic effects.

Results

In the Lehero-MG project, an intense review of the biofouling’s effect on hydrodynamic forces has been done. The main concentration was on the drag force of fixed members under the steady/oscillating currents.

In general, this study highlighted the fact that hydrodynamic forces on cylindrical members could be significantly modified introducing all of pertinent marine fouling physical parameters. Most of the previous researchers calculated the drag coefficient only based on the surface roughness ratio, particularly in the post-critical Re region. However, as proved in this project, the dependency of the biofouling only on the surface roughness is subjected to a major debate. Therefore, although most models are relying only on the relative surface roughness, the CDs should be defined as a function of several parameters. It is also showed that the drag force coefficient depends upon surface coverage percentage, relative surface roughness, biofouling species, and the aggregation pattern.

Moreover, a new approach, relying on gathered data, is proposed to calculate the drag force coefficient based on surface roughness, surface coverage ratio, aggregation type as well as biofouling species. The method is straightforward, easy to understand. The new approach gives a better understanding of the drag force coefficient behaviors compared to the previous forms. Moreover, by using the proposed approach, numerical models are able to conduct the biofouling effects in a more realistic and reliable way. Considering these concerns, the multiple parameters equation were proposed as an adequate method for estimating the drag coefficient for circular members covered with biofouling.

Methods have been tested to identify the best measure of roughness. Madogram has been shown to be the most relevant. It has also been shown that a one-centimetre variation in mussel roughness can cause a 10% increase in effort on a realistic pelvis-tested anchor configuration.

Biocolonisation on UN@SEA

Biocolmar offshore platform on UN@SEA site

Publications and papers published

Oral Communications
  • nified Approach For Estimating Of The Drag Coefficient In Offshore Structures In Presence Of Bio-Colonization, Bakhtiari A., Schoefs F., Ameryoun H. Proc. of 37th int. conf. on Offshore Mechanics and Arctic Engineering, (O.M.A.E’18), paper 78757, June 17-22, 2018, Madrid, Spain, 7 pages, proc. On CD-Rom (ASME 2018).
  • A review of the biofouling parameters influencing the drag force coefficient of offshore structures. Bakhtiari, A., Schoefs, F. & Ameryoun, H. 3rd International Conference on Renewable Energies Offshore (RENEW 2018), session Tuesday Morning ‘Wind Energy Devices I’, 8 pages, 8 – 10 October 2018, IST Congress Centre, Lisbon, Portugal, (2018).
  • Evaluation of marine growth parameters effects on offshore structures loading, Bakhtiari A., Schoefs F., Berhault C., Ameryoun H. paper #29, 54th ESReDA Seminar on Risk, Reliability and Safety of Energy Systems In Coastal and Marine Environments, organized by Université de Nantes, Sea and Litoral research Institute – FR CNRS 3473, MSH Ange Guepin, April 25th – 26th, 2018, Nantes, France (2018).
  • Assessing and modeling the thickness and roughness of marine growth for load computation on mooring lines, Schoefs, F., Bakhtiari, A., Hameryoun, H., Quillien, N., Damblans, G., Reynaud, M., Berhault, C., O’Byrne M., Floating Offshore Wind Turbine conference (FOWT 2019), session Friday Morning ‘Wind Energy Devices I’, 24 – 26 April 2019, Le Corum, Montpellier, France, (2019).
  • Marine growth: Full-scale Experimental investigations on the Dynamic Influence of Mussels on Dynamic Cable. Schoefs, F., Damblans G. ’Floating Offshore Wind Turbines’ Conference, FOWT 2020, Academic session, September 8-9 2020
  • Marine growth effect on the hydrodynamical behavior of a submarine cable under current and wave conditions. Marty, A., Berhault, C., Damblans, G., Facq, J-V., Gaurier, B., Germain, G., Soulard, T., and Schoefs F., 17èmes Journées de l’Hydraudynamique, JH2020, 24-26 Novembre 2020, Cherbourg-en-Cotentin.
Publications
  • Towards an Understanding of the Marine Fouling Effects on VIV of Circular Cylinders: Partial Coverage Issue, Zeinoddini M., Bakhtiari A., Schoefs F., Zandi A. P., Biofouling, 33:3, 268-280 – 2017.
  • Unified Approach For Estimating Of The Drag Coefficient In Offshore Structures In Presence Of Bio-Colonization. Bakhtiari A., Schoefs F., Ameryoun H. Proc. of 37th int. conf. on Offshore Mechanics and Arctic Engineering, (M.A.E’18), paper 78757, June 17-22, 2018, Madrid, Spain, 7 pages, proc. On CD-Rom (ASME 2018).
  • A review of the biofouling parameters influencing the drag force coefficient of offshore structures. Bakhtiari, A., Schoefs, F. & Ameryoun, H., Proceedings 3rd International Conference on Renewable Energies Offshore (RENEW 2018), (2019)
  • A new approach to evaluate hydrodynamic force coefficients in presence of biofouling on marine/offshore structures, Schoefs F., Bakhtiari A., Ameryoun H. , Biofouling, manuscript ID is GBIF-2018-0196, Submitted october 12th 2018, revision required.
  • Effect of roughness of mussels on cylinder forces from a realistic shape modelling, A. Marty, F. Schoefs, J-V. Facq, B. Gaurier, G. Germain, T. Soulard,  Journal of Marine Science and Engineering, section Ocean Engineering, Volume 9, Issue 6, # 558 – 2021.
  • Experimental study of marine growth effect on the hydrodynamical behaviour of a submarine cable. A. Marty, C. Berhault, G. Damblans, J-V. Facq, B. Gaurier, G. Germain, T. Soulard, F. Schoefs, Applied Ocean Research, 114 (Sept. 2021).
  • “Fractal Dimension as an Effective Feature for Characterizing Hard Marine Growth Roughness from Underwater Image Processing in Controlled and Uncontrolled Image Environments”, Schoefs F., O’Byrne M., Pakrashi V., Gosh B., Oumouni M., Soulard T., Reynaud M., Journal of Marine Science and Engineering, 2021, 9(12), 1344; doi.org/10.3390/jmse9121344 – 2021
  • Feature-Driven Modelling and Non-Destructive Assessment of Hard Marine Growth Roughness from Underwater Image Processing, Schoefs F., O’Byrne M., Pakrashi V., Ghosh B., Oumouni M., Soulard T., Reynaud M., JMSE, revision requested janv 2021.
Workshops :
  • Workshop ‘Morinson Day’ est organisé par l’UN et l’ECN le 21 novembre 2018 : il est réservé aux partenaires ANR MHM, ANR OMDYN. Durant 3 heures, il a vocation à reprendre les bases de la formulation de Morison et hypothèses associées, d’étudier les capacités d’extrapolations hors hypothèses et de disposer des éléments clés de prise en compte de la bio-colonisation dans cette formulation.
  • Workshop ‘Environmental monitoring webinar, focusing on marine life and biofouling, 1st April 2020 dans le cadre du projet Interreg Atlantic Area ‘BlueGIFT’ (Blue Growth And Innovation Fast Tracked), destiné aux sites d’essais de la façade Atlantique de l’Europe. 20 participants, essentiellement du personnel technique et de recherche, dans le but d’initier des collaborations sur ce sujet.
  • Workshop en fiabilité (F. Schoefs : Président du Comité d’Organisation et Chraiman du Technical Program Committee (20 pers.)), de 54th ESReDA Seminar on Risk, Reliability and Safety of Energy Systems In Coastal and Marine Environments, April 25-26th 2018, Nantes: 61 participants.

Prospects

  • Analysis of other species, especially flexible species
  • Dynamic Effects Analysis
  • Biocolonization SHM